Air dashpot



Jan. 13, 1959 H. N. Buss AIR DAsHPoT Filed March 8, 1954 AT RNE YS.

INVHVTOR.

States s claims. (C1. 18s-9s) The present invention relates to dashpots for retarding or checking mechanical movements, and more particularly to an improved dashpot which is adapted to operate with a compressible fluid, such as air, as a motionretarding medium.

Dashpots employing a compressible fluid as a motionretarding medium have had limited application in the past, principally because the compressible medium must becompressed a substantial amount before it develops much resistance or retarding elect. This means that the piston or equivalent medium-compressing member of the dashpot has to be displaced a substantial ydistance in the cylinder or equivalent chamber containing the compressible medium before any substantial motion-retarding elfect is developed. Such substantially unchecked displacement permits an excessive amount of substantially unrestrained travel of the piston relative to the cylinder which is obviously undesirable, and renders the dashpot unsuitable for many applications.

As a result of this difficulty, dashpots employing compressible liuids, such as air, have not been favorably regarded for many uses, even though they offer many advantages in comparison with dashpots lilled with noncompressible fluids, such as oil. For example, air dashpots, unlike hydraulic dashpots, are relatively unaifected by temperature changes and also are superior from the standpoint of freedom from lling and leakage problems, cleanliness and reduced cost of manufacture.

The principal object of the present invention, therefore, is to provide an improved dashpot adapted to be illled with a compressible fluid, such as air, and in which unretarded movement of the iiuid compressing member is substantially completely eliminated.

Another object is to provide a dashpot suitable for use with compressible lluids and in which the motion retarding force developed by the fluid medium extends 59 throughout substantially the entire stroke length of the iiuid compressing member.

Other objects will be in part obvious, and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth and the scope of the application of which will be indicated in the appended claims.

In the drawing:

Figure l is a longitudlnal sectional view of a dashpot constructed in accordance with the present invention, illustrating one extreme position of the parts thereof;

Figure 2 is a view similar to Figure l, showing the other extreme position of the parts.

Referring to the drawing,`a dashpot constructed in accordance with the present invention includes a casing or cylinder 2 which serves as a container for the motion retarding fluid, which may be a compressible iluid, and is preferably air. The cylinder is internally threaded at one end to receive an end plate 4 having an upstanding neck @which is'provded with a bore 8 perpendicular ,En qm 2,868,336 s, is Patented Jan. 13, 1959 to the axis of the cylinder to receive a pin of an anchor or the like to which the cylinder may be secured, and about which it may be pivoted, if desired. The other end of the cylinder 2 is closed by an end plate 10 having an outwardly extending neck 12 in which is provided an axially disposed throughbore 14 for accommodating a reciprocable piston rod 16. The piston rod 16 is preferably received in the bore 14 with a close sliding tit to prevent leakage of the cushioning iiuid from the cylinder 2, and the outer end of the neck 12 is counterbored to receive a packing ring 18 of oiled felt or the like for lubricating the piston rod 16 and insuring a substantially leakproof connection between the rod and the cylinder. The outer end of piston rod 16` is provided with a bore 20 forming another pivotal connection for the dashpot.

Supported for axial slidable movement in the cylinder 2 is a piston 26, which includes a support plate or disc 28, and a liexible washer 30 of leather or the like disposed on one side thereof. Preferably, the other side of the support plate 23, opposite end plate 10, is shaped in a manner complemental to plate 10, so as to provide a good surface-to-surface mating contact therewith. The support plate 2d is of suliicient diameter to fully support the washer 30, but is freely slidable within the cylinder 2. lThe support plate is provided at its center with a hollow sleeve 32 which slidably engages and is supported on the piston rod. The sleeve 32 is threaded at its outer end, as shown in Figure 2, and carries a nut 33 beneath which is retained a backing plate 34 which serves to clamp the flexible washer against the support plate.

T he washer 3) is of sufcient diameter so that, when enclosed within the cylinder, it has a longitudinally depending rim or circumferential flange 33 which engages the inside Wall of the cylinder with a sufciently fluidtight sliding connection to compress the iluid in the cylinder and retard or brake displacement of the piston in one direction, i. e.' upwardly as shown in the drawing. Qn the other hand, when the piston is displaced downwardly in the cylinder, the flange 38 of washer 30 yields sufficiently to allow the fluid to flow freely past the piston, and thus movement of the piston in this direction is substantially unretarded.

The end of the piston rod within the cylinder has a `necked-down or reduced diameter portion ilLthe junction of which with the remainder of the piston rod forms a tapered shoulder All. The sleeve 32 of support plate 28 is provided with a tapered counterbore 42 on its lower side which complements and is adapted to seat against the shoulder el, thus preventing slidable movement of the piston rod i6 relative to the piston 2.6 in the upward direction as shown in the drawing. The shoulder 41 is so located on the piston rod le as to space the piston from the end plate lil of the cylinder, when the piston rod 16 is at its innermost extreme position as shown in Figure 2, a distance somewhat less than the full length of stroke of the piston rod lo. To normally hold the piston against the shoulder 4l, and yet enable limited axial sliding movement of the piston rod 16 relative to the piston 26 in the downward direction, there is provided between the piston and piston rod an axially resilient connection in the form of a compression spring 44, one end of which engages the outer end of the sleeve 32 and the other end of which is retained by a washer @lo held on the end of the piston rod lo by a snap ring 48 or the like.

To permit controlled flow of the dashpot fluid between opposite sides ot' the piston, and thereby enableregulation of the speed of piston travel, the piston is provided with a fluid bypass, which consists of a screw Sil threaded into a hole provided in the support plate and having its head 52 received in aligned holes in the Washer and the backing plate. The screw Si? has a longitudinal bore 54, one

end of which is reduced in diameter to provide a metering bypass orifice 56 through which the fluid in the cylinder is adapted to ilow as the piston is displaced axially of the cylinder. The bypass provides a. control orice which of courseinay be mader adjustable or of'any desired-size. to provide any desired1degree of throttling of the bypass ow.

The operation ofthe dashpot will now be described. As previously described, the piston 26 is so located on the piston rod i6 as to be spaced from the end plate of the cylindera distancesomewhat less than the full stroke length .of the piston rod when the rod is at its innermost position in the cylinder 2, as shown in Figure 2. Thus, when the rod i6 is withdrawn from thecylinder in moving toward its other extremeposition, as shown in Figure l, the movement of the 4piston 26 With the rod brings the mating, surfaces of the piston 26 and end plate itt) of the cylinder into abutting or contacting relation somewhat before the piston rodreaches the end of its outward stroke. Since the bypass orifice 56 in the piston permits the fluid inthe cylinder to flow from one side of the piston to the other, and since the piston 26 is constructed so that 'iiuid in thek cylinder may iiow past the edge of the piston relatively freely during the outward stroke of the piston rod, it will be appreciated that the abutting and mating engagement of the piston 26 and end plate 10 will displace substantially all `of the lluid from between the piston and end plate. The remaining portion of the outward stroke ofthe piston rod 16 after the piston 26 abuts the end plate 10 is accommodated by the compression of the spring 44, which insures that the piston will be maintained in tightly abutting and mated engagement with the end plate 10 to prevent fluid from re-entering therebetween through the bypass orice. Provision of the axially yielding connection afforded by spring 44 also permits therod 16 to be displaced the remainder of its stroke, relative to the neck 6, without danger of injury to any portion of the'dashpot. Thus operation of the dashpot in the manner described can be obtained without the necessity of careful and exact regulation of the piston rod stroke length, to avoid inadvertent pulling of the end plate 10 out of cylinder 2, or other damage to the dashpot. The axially resilient connection provided by spring 44 also insures that any slight displacement of the piston rod 16 back into the cylinder 2, due to backlash in the equipment to which it is connected or for any other reason, will not displace the piston out of abutting engagement withrthe end plate and permit liuid to re-enter behind the piston.

With this arrangement, when the piston rod 16 is displaced back into the cylinder and the shoulder lil engages the piston 26 and moves it away from engagement with the end plate 1G, a partial vacuum is immediately formed between the piston 26 and end plate llti. The presence of this partial vacuum behind the piston creates a substantial pressure differential across the piston, even though the iiuid in the cylinder on the front side of the piston has been compressed very little, or not at all. Thus a substantial retarding force is applied to the piston 26 at the very beginning of its displacement away from the end plate 10 and well before the development of any material retarding effect by compression of the fluid in front of the piston. Of course, as the piston is further displaced away from the end plate with the further displacement of the rod into the cylinder, fluid will flow through the bypass orifice 56 and Vinto the space between the piston and end plate, and the inherent expansion of the iiuid will rapidly reduce the vacuum. By the time the vacuum has been much reduced, however, the piston will have been displaced sufficiently far in the cylinder to compress the lluid on its front side enough to develop a substantial retarding effect for the piston rod in the usual manner.

It may thus be seen that, with a dashpot constructed and operating as above described, excessive free movement of thepiston rod, or objectionable displacement of the piston into the cylinder before any retarding effect is developed, is eliminated, and a substantial motion retarding force is applied to the piston right from the start of its displacement. This immediate retarding effect resulting from the vacuum developed behind the piston, together with the retarding force developed later on by the conventional compressionofthe lluid in front of the piston, insures an ample brakingof the piston rod displacement throughout substantially the entire length of its stroke. As a result of this improved operation, dashpots employing a cheap and practicalcompressible'uid, such as air, may be used to advantage in installations where excessive free andV unrestrained movement has hitherto made their use impractical.

While the present invention-has been illustrated as applied to a dashpot in which the fluid is compressed only during movement of the piston in one direction, it will be obvious that the invention may also be employediin a dashpot of the type wherein the piston compresses. the fluid and retards the piston rod displacement in -both directions.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the -accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the language used in the following claims is intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

I claim:

l. An air dashpot comprising an air cylinder having.- sealed end walls, a reciprocal piston rod extending through one end wall, said rod having a solid portion of re.- duced cross section at its inner end terminatingf ina radial shoulder spaced from the end of the rod, a-piston slidably mounted on said portion for limited slid-ingr movement axially of the rod toward` and away from the shoulder, a spring on the rod fastened to the end of the rod and engaging the piston for biasing the piston toward said shoulder, said piston having a surface complementary .throughout to said one end wall wherebysubstantially all of the air is displaced from between the piston and said oneend wall Vwhen the piston abuts :said one end wall, and means forming a kcontinuously-openbut restricted liuid bypassthrough the piston.

2. An air dashpot comprising an air clyinder'having sealed end walls, a reciprocal piston'rod extending through one end wall, said rod having an imperforateI portion of` reduced cross section at its inner end, asingle piston slidably mounted on said portion for limited sliding movement axially of the. rod, said one end wallwhaving a planar surface facing the piston, a spring between the rod and piston biasing the piston toward .said one end wall of the cylinder, said piston comprising a plate having a planar surface complementary to said one end wall and a ilexible washer mounted on the plate, said planar surfaces being coextensive to displace substantially all-of the air between the piston and said one end` wall when brought into abutment, means forming a restricted uid bypass through the piston, and connecting means on .the cylinder and piston rod.

3. An air dashpot for uniformly controlling the speed of oppositely movingelements comprising a cylinder closed at its ends and containing air, a reciprocable piston rod in said cylinder,I a piston on said rod including a rigid ydisc of slightly less diameter than saidA cylinder and a ,flexiblewasher clamped against one side. of said disc, said washer having a diameter normally larger than said cylinder so as to form within said cylinder a resilient peripheral flange-extending Iaxiallyaway from said disc and engageable with said'cylinder during movement of said piston in one direction to compress the air therein, a continuously open but restricted fluid bypass in said piston connecting opposite sides thereof, said piston being positioned on said rod so as to abut said disc into contact with one end of said cylinder at the end ofthe stroke of said piston rod in a reverse direction opposite to said one direction, and a resilient connection between the piston and piston rod to permit overtravel of the piston rod, said disc having a surface complemental throughout to the opposed surface of said one end of said cylinder for displacing substantially all air from between the complementary surfaces of said disc and cylinder end at the end of the stroke in said reverse direction whereby disengagement of said piston from said cylinder end during the return stroke of said piston rod in said one direction creates a vacuum behind said piston for retarding movement of said rod.

4. Anair dashpot for uniformly controlling the speed of opposite relatively moving elements comprising a cylinder having end walls, a piston disposed in the cylinder for sliding movement toward and away from one end wall of the cylinder, said piston having a surface which is complementary throughout to said one end wall so that when the piston abuts said one end wall substantially no air exists between the piston and the end wall, means forming a continuously open but restricted orifice to admit air between the piston and end wall to regulate movement of Ithe piston away from said end wall, and means for connecting the cylinder and piston to oppositely relatively moving elements permitting limited relative movement of the elements after the piston and said one end wall engage.

substantially all of the air therebetween and form a vacu` um when the piston abuts said one end of the cylinder, a flexible washer attached to and carried by the piston in engagement with the side wall of the cylinder rearwardly of said end face of the cylinder to prevent the passage of air around the periphery of the piston as the piston is moved away from said end wall of the cylinder, a piston rod connected to the piston `and extending through an end wall of the cylinder, and means forming a continuously op-en but restricted orifice to admit air between the piston and said end wall to regulate movement of the piston away from said end Wall.

References Cited in the l'ile of this patent UNITED STATES PATENTS 1,198,829 Edwards Sept. 19, 1916 1,427,764 Stuebins et al. Aug. 29, 1922 1,488,197 Demke et al Mar. 25, 1924 1,588,780 Stanzel et al lune 15, 1926 1,736,410 Longwell Nov. 19, 1929 2,091,904 Baumann Aug. 3l, 1937 FOREIGN PATENTS 656,057 GreatBritain Aug. 8, 1951 

